Autarkes feldgerat order autarker funkadapter furein feldgerat der automatisierungstechnik

ABSTRACT

The invention relates to an autarkic field device or an autarkic radio adapter ( 2 ) for a field device ( 1 ), of automation technology fed with limited energy via an energy supply unit ( 3 ) associated, or associable, with the field device ( 1 ) or the radio adapter ( 2 ), characterized in that, between the energy supply unit ( 3 ) and an internal voltage source ( 4 ), whose voltage exceeds, or at times can exceed, the voltage of the energy supply unit ( 3 ), a barrier ( 5   a;    5   b ) of at least one diode group having at least two diodes ( 6 ) connected in parallel is arranged, which blocks flow of electrical current from the internal voltage source ( 4 ) to the energy supply unit ( 3 ) or to the connection terminals ( 7 ) of the field device ( 1 ) or of the radio adapter ( 2 ) for the energy supply unit ( 3 ).

FIELD DEVICE OF AUTOMATION TECHNOLOGY

The invention relates to an autarkic field device or an autarkic radioadapter for a field device of automation technology, which is fed withlimited energy via an energy supply unit associated, or associable, withthe field device or radio adapter.

In process automation technology, field devices are often applied, whichserve to register and/or influence process variables. To registerprocess variables, sensors serve as, for example, fill level measuringdevices, flow measuring devices, pressure and temperature measuringdevices, pH-redox potential measuring devices, conductivity measuringdevices, etc., which register the corresponding process variables, filllevel, flow, pressure, temperature, pH-value, or conductivity. Servingto influence process variables are actuators, such as, for example,valves or pumps, via which the flow of a liquid in a pipeline section,or the fill level in a container can be changed. In principle, alldevices, which are applied near to the process and which deliver orprocess the process relevant information, are referred to as fielddevices. Besides sensors and actuators, generally also referred to asfield devices are any units, which are directly connected to a fieldbusand which serve for communication with superordinated units, e.g. asremote I/Os, gateways, linking devices, and wireless adapters. Amultiplicity of such field devices are produced and sold by theEndress+Hauser group.

In modern industrial plants, field devices are, as a rule, connectedwith superordinated units via bus systems (Profibus®, Foundation®Fieldbus, HART®, etc.). Normally, superordinated units involve controlsystems or control units, such as, for example, a PLC (programmablelogic controller). The superordinated units serve, among other things,for process control, process visualization, process monitoring as wellas start-up of the field devices. The measured values registered by thefield devices, especially sensors, are transmitted via the connected bussystem to one or, in given cases, also to a number of superordinatedunits. Along with that, a data transmission from the superordinated unitvia the bus system to the field devices is also required; such datatransmission serves especially for configuring and parametering fielddevices or for diagnostic purposes. Generally stated, the field deviceis serviced from the superordinated unit via the bus system.

Besides hardwired data transmission between the field devices and thesuperordinated unit, the possibility of wireless data transmission alsoexists. Especially in the bus systems Profibus®, Foundation® Fieldbusand HART®, wireless data transmission via radio is provided for byspecification. Additionally, radio networks for sensors are specified inthe standard IEEE 802.15.4 in greater detail. For implementing wirelessdata transmission, newer field devices, especially sensors andactuators, are, in part, embodied as radio field devices. These have, asa rule, a radio unit and an electrical current source as integralcomponents. In such case, the radio unit and the electrical currentsource can be provided in the field device itself or in a radio moduledurably connected to the field device. Through the electrical currentsource, an autarkic energy supply is enabled in the field device.

Besides this, there is the opportunity to turn field devices withoutradio units into radio field devices, by coupling with a wirelessadapter, which has a radio unit. A corresponding wireless adapter isdescribed, for example, in the publication WO 2005/103851 A1. Thewireless adapter, as a rule, is releasably connected to a fieldbuscommunication interface of the field device. Via the fieldbuscommunication interface, the field device can transmit the data to betransferred via the bus system to the wireless adapter, which thentransmits these via radio to the target location. Conversely, thewireless adapter can receive data via radio and forward it via thefieldbus communication interface on the field device. Supplying thefield device with electrical power occurs then, as a rule, via an energysupply unit of the wireless adapter.

In the case of autarkic radio field devices and wireless adapters, thecommunication, for example with a superordinated unit, is conducted as arule via the wireless interface of the radio field device or thewireless adapter. Additionally, such radio field devices or wirelessadapters have, as a rule, a hardwired communication interface. Forexample, in the HART® standard, it is provided that radio field devicesmust also have a hardwired communication interface, in addition to awireless interface. Via such a hardwired communication interface, forexample, on-site configuration of the radio field device or the wirelessadapter is possible via a service unit, such as, for example, a handheldcommunicator connected to the hardwired communication interface.Additionally, the hardwired communication interface can be embodied as afieldbus communication interface, so that the communication is conductedthere across according to a bus system, such as, for example, accordingto one of the standardized bus systems, Profibus®, Foundation® Fieldbusor HART®. Via such a fieldbus communication interface, the radio fielddevice or the wireless adapter can also be connected to a correspondinghardwired fieldbus.

The energy supply unit or the electrical current source of a wirelessadapter or a radio field device is, for example, a disposable batteryprovided in the wireless adapter or the radio field device, a fuel cell,a solar energy supply, and/or a rechargeable battery.

If field devices or radio adapters are fed from an energy supply unitwith limited energy supply, problems regarding sufficient explosionprotection can occur. Problems show themselves as soon as the fielddevice or the radio adapter needs to be connected to a higher voltagesource, or when assemblies present in the field device or in the radioadapter produce higher voltages than the energy supply unit. In thiscase, the voltage supplied part of the field device or radio adaptermust have a barrier, which fulfills the following two tasks:

-   -   prevention of an electrical current flowing back to the energy        supply unit    -   protection against wrong connections.

In the explosion endangered region, supplementally, the followingrequirements must be fulfilled:

-   -   prevent spark formation in the case of disconnection of the        energy supply unit    -   sealing-off internal charge storers or voltage sources from the        outside.

A known solution for the above-mentioned problem provides a barrier ofdiodes connected in series. For example, through a series circuit ofthree diodes, the explosion protection type ex-ia can be implemented.The disadvantage of the known solution is to be seen in the fact thatthe voltage drop across the diodes leads to a relatively high powerloss, which reflects negatively on the lifetime of the energy supplyunit, especially the battery. The voltage drop becomes greater withincreasing electrical current flowing from the battery.

Another known solution that solve parts of the above-mentioned tasksprovides electronic circuits, which usually are integrated in a circuitand generally referred to as “ideal diodes”. In these circuits, theelectrical current flow direction is ascertained and the electricalcurrent, in the case of wrong flow direction, is interrupted by means ofa switch, e.g. by means of an FET. The disadvantage of this method isthe relatively long reaction time of the circuits: In the case ofdisconnecting the battery, there is the danger of spark formation, whichcan have catastrophic consequences in explosion-endangered regions.Through the too-slow reaction of these circuits, charge quantitiesgreater than 40 μJ can also penetrate these barriers, which is notallowable in regions of explosion protected environments.

Based on the earlier described state of the art, an object of theinvention is to provide an apparatus which minimizes the voltage dropand therewith the lost power for field devices, which have a limitedenergy supply available.

The object is achieved by the feature that, between the energy supplyunit and an internal voltage source, whose voltage exceeds, or, attimes, can exceed, the voltage of the energy supply unit, there isarranged a barrier of at least one diode group having at least twodiodes connected in parallel for blocking flow of electrical currentfrom the internal voltage source to the energy supply unit, or to theconnection terminals of the field device or of the radio adapter for theenergy supply unit. Across the at least two parallel connected andequally constructed diodes, the voltage drop is almost equal, and theelectrical current divides itself at least approximately equally to theat least two diodes. In this way, the effect of the voltage increase isreduced in the case of increasing electrical current. In the case ofparallel circuits of diodes, in contrast to the known series circuits,there is a marked reduction of the effect of the forward voltageincrease under load. Furthermore, according to the invention, it isachieved that only a limited, maximum allowable energy amount gets intothe process, upon disconnecting of the battery from the field device orfrom the adapter. Thus the apparatus of the invention is also applicablein the explosion endangered region.

An advantageous embodiment provides, that a radio module is associatedwith the field device or the radio adapter and that the field devicecommunicates via the radio module and a radio network with asuperordinated control unit. Furthermore, it is provided, in thisrelationship, that the radio module is integrated in the radio adapteror in a wireless adapter, which is connected with the field device via afirst interface provided on the field device and a second interfaceprovided on the radio adapter, together with corresponding connectinglines. Further details for this are presented below.

Alternatively, it is provided that the field device does not have itsown energy supply, but instead is fed externally via the radio adapter.In such case, the energy supply unit is integrated in the radio adapter,and the data exchange and the energy supply occur between the energysupply unit and the radio adapter via the same two connecting lines.Further details for this are presented below.

In the case of an autarkic field device or an autarkic radio adapter,the energy supply unit is preferably integrated directly in the fielddevice. Further details for this are presented below.

An especially advantageous embodiment of the field device of theinvention, or the radio adapter of the invention, provides that thebarrier is composed of three diode pairs connected in series, whereinthe diodes of a diode pair are connected in parallel. With thisembodiment, the explosion protection type ex-ia can be implemented. Thisexplosion protection type calls for a triple redundance of the diodes,which means that in the case of the failure of two diodes, correctfunctioning of the circuit is always still assured.

Preferably, the diodes are Schottky diodes. An example of the Schottkydiodes are type MBR0520. Schottky diodes have the advantage, compared toother diodes, that the voltage drop is relatively small through them andthat they have a relatively fast reaction time.

Advantageously, the diodes in the diode pairs, or the diode groups, areso embodied, that in the case of a disconnection of the energy supplyunit from the field device or the radio adapter, a maximum 40 μJ or 40μVAs reach the connection terminals of the field device, or theconnection terminals of the radio adapter, especially the connectionterminals of the associated energy supply unit.

preferred as energy supply unit, in connection with the invention, is adisposable battery. Alternatively, a fuel cell, a solar energy supply,or a rechargeable battery can also be used.

As already described above, in connection with the invention, thecommunication between the field device or the radio adapter and thesuperordinated control unit can also occur based on one of thecommunication protocols customary in automation technology.

The invention will now be explained in greater detail on the basis ofthe appended drawing, the figures of which show as follows:

FIG. 1 a schematic representation of a radio network having a pluralityof field devices;

FIG. 2 a block diagram of a preferred embodiment of the wireless adapterof the invention;

FIG. 3 a schematic representation of the apparatus of the invention;

FIG. 4 a barrier of three diode groups connected in series, wherein eachdiode group is composed of n diodes connected in parallel; and

FIG. 5 a barrier of three diode groups connected in series, wherein eachdiode group is composed of two diodes connected in parallel.

FIG. 1 shows a radio network having a plurality of field devices 1, eachembodied as a radio field device, and a gateway G. The field devices 1are connected among one another and with the gateway G, in each case, byradio connections RC, which is indicated in FIG. 1 by the dashed lines.Because the field devices 1 and the gateway G are, in each case,connected via a number of radio connections RC, in the case of a failureof one of the radio connections RC, the communication can be maintainedvia one of the other radio connections RC.

Frequency Hopping Spread Spectrum (FHSS) or Direct Sequence SpreadSpectrum (DSSS) methods, for example, are suitable as radio transmissiontechnologies for the radio connections RC. Due to the required smalltransmission powers, Ultra Wide Band-technology (UWB) is also very wellsuited.

The gateway G can also be a long distance transmission unit, e.g. theproduct “Fieldgate” of the firm, Endress+Hauser. In this case, thegateway G can communicate worldwide, for example via Internet, GSM orpublic switched telephone network, with a superordinated unit.Additionally, a (not illustrated) superordinated unit and/or a (notillustrated) servicing device can also communicate directly via acorresponding radio connection with the illustrated radio network.

FIG. 2 presents a schematic representation of a preferred embodiment ofthe wireless adapter of the invention 2. In the illustrated example, aconventionally embodied field device 1 is connected via a connectingline 14 with the wireless adapter 2. By connection of the wirelessadapter 2, the field device 1 becomes a radio field device, and can be,for example, one of the field devices 1 shown in FIG. 1.

The field device 1 is composed of a measured value transducer, orsensor, 15 and a measurement transmitter 16. The field device 1—asalready presented at length earlier—can be designed for determiningand/or influencing any number of process variables.

Arranged in the radio adapter 2, preferably on a circuit board, arevarious components. Via an interface 12 and the connecting lines 14, theradio adapter 2 is connected with the measurement transmitter 16.Connected with the interface 12 is an component group 4 for voltageconversion and a communication module 8, or a communication interface 8,as the case may be. In the sense of the invention, the component groupfor voltage conversion is an internal voltage source 4. The componentgroup 4 for voltage conversion is connected with the communicationmodule 8 and the microprocessor 9.

The field device 1 and the wireless adapter 2 are connected together forcommunication. In the case of the hardwired communication interface 7 a,7 b, such involves, preferably, a HART® communication interface.Associated with the communication interface 7 a, 7 b is a functionalunit, which performs the sending and/or receiving of digital signals(e.g. corresponding to the HART® standard) via the communicationinterface 7 a. Via the communication interface 7 a, the field device1—alternatively to the illustrated connection on the wireless adapter2—can also be connected to a hardwired fieldbus system, which usesconventional automation technology, e.g. a HART® fieldbus system.

Additionally, the field device 1 includes, likewise not shown, amicroprocessor and a data memory, in which, among other things,parameters of the field device 1 are stored. Accessing of the datamemory occurs via the microprocessor. For servicing the field device 1on-site, provided on the field device 1 is usually, likewise notseparately shown, a display and service unit, which is in communicationconnection with the microprocessor.

The wireless adapter 4 includes, as already mentioned, a control unit inthe form of a microprocessor 9. For data exchange via the radio networkRN, the microprocessor 9 is connected with a radio unit 10, which has aRF-chipset, and an antenna 11. The radio unit 10 is, in such case,embodied in such a manner, that the wireless communication occursaccording to a conventional automation technology standard, preferablyaccording to the HART®standard. The microprocessor 9 is additionallyconnected with, not separately illustrated, a data memory, in which,among other things, parameters of the wireless adapter 2 are stored. Forcommunication with the field device 1, the wireless adapter 2 includes ahardwired communication interface 7 b, with which in turn, there isassociated a functional unit, which performs the sending and/orreceiving of digital signals via the communication interface 7 b.

In the case of the arrangement illustrated in FIG. 2, the communicationinterfaces 7 a of the field device 1 and the communication interface 7 bof the wireless adapter 2 are connected with one another via a2-conductor connecting line 14. Via this connection, both thecommunication between the field device 1 and the wireless adapter 2occurs, as well as also the electrical current supply of the fielddevice 1 by the wireless adapter 2.

For the purpose of providing the electrical current supply for the fielddevice 1 and the wireless adapter 2, the wireless adapter 2 isassociated with an energy supply unit 3. The energy supply unit 3 isable to supply the field device 1, or the radio adapter 2 and the fielddevice 1, with limited energy. The energy supply unit 3 is e.g. adisposable battery, a rechargeable battery, a solar panel, or a fuelcell. In the case of the illustrated field device 1 or the illustratedradio adapter 2, involved, thus, are energy autarkic units.

FIG. 2 presents the case in which the radio module 10 is integrated in aradio adapter 2. Through connection of the radio adapter 2 to theconventional field device 1, the field device 1 can be retrofitted intoa radio field device. Of course, the radio module 10 can also beintegrated directly into the field device 1.

According to the invention, at least one barrier 5 a, 5 b is provided,which blocks a flow of electrical current from the internal voltagesource 4 back to the energy supply unit 3, or to the connectionterminals 7 a of the field device 1, or to the connection terminals 7 bof the radio adapter 2 for the energy supply unit 3. In the case of theform of embodiment of the apparatus of the invention illustrated in FIG.2, a barrier 5 a is arranged between the component group 4 for voltageconversion and the energy supply unit 3. Another barrier 5 b is providedbetween the interface 12 and the measurement transmitter 16.

The barriers 5 a, 5 b, in the illustrated case, are composed of threediode groups connected in series and having, in each case, two diodes 6connected in parallel. By, in each case, the parallel connection of twoequal diodes 6, the voltage drop across the diodes 6 is approximatelyequal, and the applied electrical current on the parallel diodes dividesitself at least almost equally. In this way, a smaller power loss can beachieved, which results in an increased lifetime of the battery, orenergy supply unit, 3. Through the serial arrangement of three diodepairs, which corresponds to a triple redundance, the explosionprotection type ex-ia can, in turn, be implemented.

The diodes are preferably Schottky diodes. Schottky diodes distinguishthemselves by a relatively low voltage drop of 0.2-0.5V per diode atrelatively fast switching times.

FIG. 3 is a schematic representation of the autarkic field device of theinvention or the autarkic radio adapter of the invention. The componentgroup 4, which is not permitted to have any reaction on the energysupply unit 3, involves, for example, the main circuit board of theradio adapter 2. In order to assure that no electrical current flowsfrom the component group 4 back to the energy supply unit 3, the barrier5 a is provided, which is embodied as shown in FIG. 5. In order that themain board of the radio adapter 2 has no reaction on the measurementtransmitter 16, the barrier 5 b is connected between them.

The term ‘reaction’ means, in reference to the use of the field deviceor the radio adapter in an explosion endangered region, an electricalcurrent, which transports a charge greater than Q=I×t=40 μJ from thecomponent group 4 to the energy supply unit or from the component group4 to the measurement transmitter 16.

FIG. 4 presents an alternatively embodied barrier, composed of threediode groups connected in series, wherein each diode group includes ndiodes 6 connected in parallel.

LIST OF REFERENCE CHARACTERS

-   1 field device-   2 radio adapter, or wireless adapter-   3 energy supply unit-   4 internal voltage source-   5 a barrier-   5 b barrier-   6 diode-   7 a connection terminal-   7 b connection terminal-   8 communication module/communication interface-   9 microprocessor-   10 radio module-   11 antenna-   12 interface-   13 control unit-   14 connecting line-   15 measuring transducer/sensor-   16 measurement transmitter-   G gateway-   RN radio network-   RC radio connection

1. Autarkic field device, or autarkic radio adapter (2) for a fielddevice (1), of automation technology fed with limited energy via anenergy supply unit (3) associated, or associable, with the field device(1) or the radio adapter (2), characterized in that, between the energysupply unit (3) and an internal voltage source (4), whose voltageexceeds, or at times can exceed, the voltage of the energy supply unit(3), a barrier (5 a; 5 b) of at least one diode group having at leasttwo diodes (6) connected in parallel is arranged, which blocks a flow ofelectrical current from the internal voltage source (4) back to theenergy supply unit (3) or to the connection terminals (7) of the fielddevice (1) or of the radio adapter (2) for the energy supply unit (3).2. Field device as claimed in claim 1, characterized in that, associatedwith the field device (1) or the radio adapter (2) is a radio module(10) and the field device (1) communicates via the radio module (10) anda radio network (RN) with a superordinated control unit (13).
 3. Fielddevice as claimed in claim 2, characterized in that the radio module(10) is integrated in the radio adapter (2), or in a wireless adapter,which is connected with the field device (1) via a first interface (7 a)provided on the field device (1) and a second interface (7 b) providedon the radio adapter (2) and corresponding connecting lines (14). 4.Field device as claimed in claim 3, characterized in that the energysupply unit (3) is integrated in the radio adapter (2), and dataexchange and energy supply between the energy supply unit (3) and theradio adapter (2) occur via the same two connecting lines.
 5. Fielddevice as claimed in claim 1, characterized in that the energy supplyunit (3) and the radio module (10) are integrated in the field device(1).
 6. Field device as claimed in claim 1, characterized in that thebarrier (5 a, 5 b) is composed of three diode pairs connected in series,wherein the diodes (6) of a diode pair are connected in parallel. 7.Field device as claimed in claim 1 or 5, characterized in that thediodes (6) are Schottky diodes.
 8. Field device as claimed in one ormore of claim 1-3 or 5-6, characterized in that the diodes (6) of thediode pairs, or the diode groups, are so embodied that, in the case of adisconnection of the energy supply unit (3) from the field device (1) orfrom the radio adapter (2), a maximum 40 μJ, or 40 μVas, reachconnection terminals (7 a) of the field device (1), or connectionterminals (7 b) of the radio adapter (2), especially to the connectionterminals of the associated energy supply unit.
 9. Field device asclaimed in claim 1, 3, 4 or 7, characterized in that the energy supplyunit (3) is a disposable battery, a fuel cell, a solar energy supply, ora rechargeable battery.
 10. Field device as claimed in claim 1,characterized in that communication between the field device (1) or theradio adapter (2) and the superordinated control unit (13) occurs basedon a communication protocol customarily used in automation technology.